Often, fasteners used to assemble performance critical components are tightened to a specified torque level to introduce a “pretension” in the fastener. As torque is applied to the head of the fastener, beyond a certain level of torque the fastener begins to stretch. This stretch results in the pretension in the fastener which then holds the components together. A popular method of tightening these fasteners is to use a torque wrench. Accurate and reliable torque wrenches help insure the fasteners are tightened to the proper torque specifications.
Torque wrenches vary from simple mechanical types to sophisticated electronic types. Mechanical type torque wrenches are generally less expensive than electronic ones. There are two common types of mechanical torque wrenches, beam and clicker types. With a beam type torque wrench, a beam bends relative to a non-deflecting beam in response to the torque being applied with the wrench. The amount of deflection of the bending beam relative to the non-deflecting beam indicates the amount of torque applied to the fastener. Clicker type torque wrenches work by preloading a snap mechanism with a spring to release at a specified torque, thereby generating a click noise.
Electronic torque wrenches (ETWs) tend to be more expensive than mechanical torque wrenches, and more accurate as well. When applying torque to a fastener with an electronic torque wrench, the torque readings indicated on the display device of the electronic torque wrench are proportional to the pretension in the fastener due to the applied torque. However, the readings also depend on, among other factors, the under head friction between the head of the fastener and the adjacent surface of the component and the friction between the mating threads. Static friction is greater than dynamic friction. Therefore, when torquing operations are initiated, increased amounts of torque may be required to overcome static friction forces and initiate rotation of the fastener. Therefore, it follows that torque is preferably applied to the fastener in a slow and continuous manner to allow friction forces to stabilize, to help insure accuracy and to help prevent over-torquing. As well, it is often desirable for the user to see both the current torque value (torque being applied at that instant) and the peak torque value (maximum torque applied up to the present instant) simultaneously. However, existing torque wrenches typically display only the current torque value or the peak torque value at any given time.
When a torque wrench is operated in a “tracking mode,” the current torque value is displayed and the user therefore does not necessarily get immediate feedback regarding the actual peak torque value to which the fastener may have been subjected. Although with some electronic torque wrenches it is possible to get this information by downloading the data, this action is typically not instantaneous and, therefore, the operator does not get immediate feedback. On the other hand, when operating in a “peak hold mode,” the display of the electronic torque wrench typically shows only the maximum torque applied to the fastener up to that time. In the peak hold mode, the user is often ignorant of the current torque level, which can lead to either over or under-torquing the fastener.
Another factor that can affect the accuracy of a reading on an electronic torque wrench is the operating temperature. Strain gages that are used in electronic torque wrenches to measure applied torque are often affected by temperature. Therefore, to obtain accurate torque measurements, it is often necessary to measure the existing temperature and adjust the displayed torque value for a given strain gauge reading.
Drawbacks present in prior art electronic torque wrenches may lead to the over or under-torquing of fasteners, which can contribute to reduced performance, and eventual failure, of the fasteners.
The present invention recognizes and addresses the foregoing considerations, and others, of prior art constructions and methods.